The present invention relates to a novel positive-working photosensitive resin composition or, more particularly, to a positive-working photosensitive resin composition of high sensitivity capable of giving a patterned photoresist layer which is excellent in the contrast of the images, focusing latitude and orthogonality of the cross sectional profile of the line pattern as well as in the heat resistance so as to be useful as a photo-resist composition for the ultra-fine patterning works on a substrate in the manufacture of various kinds of semiconductor devices such as ICs, LSIs and the like.
As is well known, the process of photolithographic patterning is widely practiced in the manufacturing process of semiconductor devices such as ICs, LSIs and the like. In the photolithographic patterning work, a layer of a photoresist composition is formed on the surface of a substrate such as a semiconductor silicon wafer and the photoresist layer is exposed pattern-wise to actinic rays such as ultraviolet light through a transparency mask bearing the desired pattern for the semiconductor device to form a latent image of the pattern which is then developed by using a developer solution to give a patterned resist layer to serve as a protecting mask for the substrate surface in the subsequent treatment of etching and the like. Photoresist compositions are classified into negative-working ones and positive-working ones depending on the behavior of the photosensitive resin composition against irradiation with actinic rays. Positive-working photoresist compositions of the most widely used type are those comprising an alkali-soluble novolac resin as the film-forming constituent and a photosensitizing agent which is a quinone diazide group-containing compound or, in particular, an aromatic polyhydroxy compound esterified with naphthoquinone-1,2-diazide sulfonic acid.
The above mentioned aromatic polyhydroxy compound is usually selected from those having a plural number of hydroxy groups per molecule such as gallic acid esters and polyhydroxy benzophenones. Various kinds of naphthoquinone 1,2-diazide sulfonic acid esters have been heretofore proposed for the purpose including those disclosed in U. S. Pat. Nos. 3,046,118, 3,106,465 and 3,148,983 and Japanese Patent Publications No. 37-18015 and No. 62-28457.
The positive-working photoresist compositions of the prior art comprising a naphthoquinone 1,2-diazide sulfonic acid ester of a polyhydroxy benzophenone compound, however, are not always quite satisfactory in their performance relative to the sensitivity, contrast of the images, cross sectional profile of line patterns and heat resistance in order to comply with the requirements in the modern manufacturing processes of semiconductor devices involving an extremely fine photolithographic patterning work. Japanese Patent Kokai No. 1-189644 proposes an improved positive-working photoresist composition suitable for ultra-fine patterning works, in which the photosensitizing agent is a naphthoquinone 1,2-diazide sulfonic acid ester of a specific tris(hydroxyphenyl) methane compound instead of the conventional polyhydroxy benzophenone compound. This positive-working photoresist composition, however, is still not quite satisfactory in respect of the heat resistance of the patterned resist layer and in respect of the storage stability of the coating solution of the composition sometimes to cause precipitation of the photosensitizing agent. Furthermore, it is a requirement for the positive-working photosensitive resin composition in recent years that the layer of the photosensitive resin composition should have a so-called focusing latitude as large as possible in order to comply with varied depth of focus in the exposure of the layer to light depending on the difference in the thickness of the photosensitive layer.